The present invention relates to methods of making polymers containing dispersed nanoparticles of a platinum group metal, such as palladium, and containers made from the polymer-platinum group metal nanoparticle blends, which exhibit high oxygen scavenging properties and high clarity.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
Oxygen-sensitive food products including, for example, tomato-based ketchups, sauces, etc., and beverage products, such as orange juice, beer, green tea, etc., require a packaging material with high oxygen barrier properties or blocking oxygen ingress into the packaging in order to preserve the freshness and flavor of the package contents over time. Although metal cans and glass jars have traditionally been used as oxygen-impervious containers, there is a desire to use plastic containers, for example, due to their durability and strength. Plastic containers typically only offer moderate gas barrier properties, however. Plastic containers may also exhibit haze or poor clarity. For example, undesirable haze may result from the immiscibility of the polymer materials or other ingredients. Blends of dissimilar chemical structures can lead incompatibility, phase separation, and ultimately, poor clarity. Thus, there is a desire to produce plastic packaging materials (e.g., films, bottles, containers) which exhibit both high oxygen scavenging properties and high clarity and transparency.
U.S. Publication No. 2010/0028499 describes containers having walls made of a polymeric matrix where a catalyst for catalyzing the reaction of hydrogen with oxygen is dispersed in the polymeric matrix. The catalyst may be incorporated into the polymeric matrix during melt processing, for example, after the polymer has been formed.
It is believed that such blending techniques with a pre-formed polymer can result in a number of drawbacks. First, the decomposition products or volatiles of the catalyst precursor and any possible liquid carriers may remain in the resulting polymer unless the polymer undergoes some further processing, such as vacuum stripping. Second, because of the high melt viscosity of the pre-formed polymer, the uniformity of the catalyst mixing and distribution is not assured at low catalyst levels, which could result in non-uniform scavenging performance from container to container. Third, the polymer may not exhibit good clarity or transparency due to the poor mixing as descried above and the resulting catalyst particle aggregates of large size.